Typically, a known multi-type air conditioning device installed in a building including multiple rooms has a refrigerant circuit to which an outdoor unit and multiple indoor units are connected with an interconnecting pipe for providing a vapor compression refrigeration cycle. (See, for example, PATENT DOCUMENT1.) In the multi-type air conditioning device, the interconnecting pipe includes: a liquid main pipe connected to the outdoor unit, and liquid branch pipes branching off from the liquid main pipe and each connected to a corresponding one of the indoor units; and a gas main pipe connected to the outdoor unit, and gas branch pipes branching off from the gas main pipe and each connected to a corresponding one of the indoor units.
Moreover, the air conditioning device cited in PATENT DOCUMENT1 saves energy by obtaining required capacity of an indoor unit and controlling operational capacity of the compressor and a volume of air from an indoor fan, so that a refrigerant temperature (an evaporation temperature or a condensing temperature) of an indoor heat exchanger is brought to a target temperature, depending on the required capacity. Specifically, the air conditioning device cited in PATENT DOCUMENT1 controls, for example, the operational capacity of the compressor so that a refrigeration cycle is provided at the target evaporation temperature and the target condensing temperature, while changing in the energy-saving operation the target evaporation temperature and the target condensing temperature for every predetermined time period depending on the required capacity of the indoor unit.
When a compressor of the refrigerant circuit is activated in the air conditioning device, portion of refrigerating machine oil, stored in the compressor for lubricating a compression mechanism and a bearing in the compressor, flows out of the compressor together with a refrigerant and circulates in the refrigerant circuit. Here, in liquefied portion of the refrigerant in the refrigerant circuit, the refrigerating machine oil flows in the circuit together with the refrigerant; however, in gaseous portion of the refrigerant, portion of the refrigerating machine oil adheres to interior surfaces of a heat exchanger tube of a heat exchanger and a refrigerant pipe. Furthermore, when a flow rate of the gaseous refrigerant is high, the refrigerating machine oil that adhered to the interior surfaces of the heat exchanger tube and the refrigerant pipe is pushed by the gaseous refrigerant, flows inside the refrigerant circuit, and returns to the compressor. When the flow rate of the gaseous refrigerant is low, however, the refrigerating machine oil stays adhered to the interior surfaces of the heat exchanger tube and the refrigerant pipe, and fails to return to the compressor. Thus, this kind of air conditioning device typically performs oil collecting operation which involves increasing the flow rate of the gaseous refrigerant with every time period set on a timer, and collecting the refrigerating machine oil into the compressor.